1. Field of the Invention
The invention relates generally to processes for producing blends of tackifying resins and polyphenylene ether resins, preferably low molecular weight polyphenylene ether resins, that provide advantages in reducing processing temperatures and the number of processing steps during production of thermoplastic elastomer formulations which involve both components as additives.
2. Brief Description of the Related Art
Polyphenylene ether resins (PPE) are polymers of high performance engineering thermoplastics having relatively high molecular weights and possessing high melt viscosities and softening points--i.e., Tg equals 150-210.degree. C., viscosity greater than about 40.times.10.sup.4 poise at 200.degree. C. It is known in the art that properties of the polyphenylene ether resins can be materially altered by blending them with other resins. Low molecular weight polyphenylene resin is much preferred over the commercially available higher molecular weight resin in certain applications, since it has been known that adhesives containing the lower molecular weight resin have higher service temperatures.
A number of composition patents are related to blends of thermoplastic elastomers, PPEs, and tackifiers, with or without additional components in the blend. For example, in Hanson, U.S. Pat. No. 4,104,323, an adhesive composition is prepared by melt blending a PPE resin, a styrene-diene block copolymer, and a tackifying resin without the use of a solvent and at a temperature that does not result in damage to the block copolymer. This patent teaches melt blending the PPE with the tackifying resin prior to to combining with the styrene-diene block copolymer. Further, it is taught that very high PPE quantities are not preferred due to limitations in mixing.
Akiyama, U.S. Pat. No. 4,772,657, disclosed that compositions of hydrogenated block copolymer with super-high-molecular-weight high density polyethylene, when combined with the polyphenylene ether resin and the oil, give rubber-like compositions superior in the oil resistance and compression set at 100.degree. C.
Vermeire, U.S. Pat. No. 5,278,220, disclosed a polymeric composition containing a block copolymer, a thermoplastic engineering polymer and a poly(alkylene) plasticizer of a particular type. These compositions exhibited improved physical properties including retention during aging of tensile strength, color stability and low volatility upon exposure to heat and/or light.
Chu, Intl. Pat. Appl. WO 97 11,997, Apr. 3, 1997, disclosed use of a preblend of polyphenylene ether and a resin compatible with the B-block of an A-B-A block copolymer as a means of delivering more polyphenylene ether into adhesive formulations comprised of these materials.
The above references teach a number of polymeric compositions used for a number of purposes. A principal problem with the compositions of the above references is that the conventional processing technique is not as efficient and more expensive than the present invention because of the increased use of energy expended to make the polymeric composition. The conventional process technique consists of isolating each resin from a solvent by devolatization, evaporation, precipitation, and/or stripping before combining both of the resins together. To obtain a mixture of these two resins the help of heat at high temperatures is required. The temperatures involved in melt-blending the components also leads to degradation and crosslinking of the resins. Thus, it would be an advantage to process these compositions at a more efficient rate and at less energy in a way to protect the integrity of the resulting polymeric compositions.
A new improved process has been discovered that permits blending of tackifying resins and PPE, preferably low molecular weight PPE, at a reduced processing temperature, and reduced processing steps during the production of thermoplastics elastomer formulations which involve both components as additives.